JP2013214777A - Method of manufacturing optoelectronic device having bulk heterojunction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an organic optoelectronic device having a bulk heterojunction.SOLUTION: A method of manufacturing an optoelectronic device includes the processes of: depositing a first layer having protrusions over a first electrode; depositing a second layer on the first layer such that the second layer is in physical contact with the first layer; and depositing a second electrode over the second layer to form the optoelectronic device. The first layer includes a first organic small molecule material, and the smallest lateral dimension of the protrusions is between 1 to 5 times the exciton diffusion length of the first organic small molecule material. A method of manufacturing an organic optoelectronic device having a bulk heterojunction is also provided so as to include the processes of: depositing a first layer with protrusions over an electrode by organic vapor phase deposition; and depositing a second layer on the first layer, while the interface of the first and second layers forms a bulk heterojunction and another electrode is deposited over the second layer.

Description

[Cross-reference to related applications]
The present invention is a continuation-in-part of US patent application Ser. No. 10 / 824,288 filed on Apr. 13, 2004 in the name of a method for manufacturing an optoelectronic device having a bulk heterojunction. Incorporated herein by reference.

  The present invention generally relates to a method for manufacturing an optoelectronic device. More specifically, it is directed to a method for manufacturing an optoelectronic device including a bulk heterojunction.

  Optoelectronic devices rely on the optical and electrical properties of materials for generating or detecting electromagnetic radiation or for generating electricity from ambient electromagnetic radiation. Photoelectric optoelectronic devices convert electromagnetic radiation into electrical power. Photovoltaic (PV) devices or solar cells are a type of photoelectric optoelectronic device, and are particularly used to generate electrical power. PV devices generate power from light sources other than the sun, for example, to drive power consuming loads to provide light or heat, or to operate electrical equipment such as computers or remote monitoring or communication equipment Used. These power generation applications often include battery charging or other energy storage devices so that the equipment continues to operate when direct light from the sun or other ambient light source is not available. As used herein, the term “resistive load” refers to any power consumption or storage device, device or system. Another type of photoelectric optoelectronic device is a photoconductor cell. In this function, the signal detection circuit monitors the resistance of the device to detect changes due to light absorption. Another type of photoelectric optoelectronic device is a photodetector. In operation, the photodetector has an applied voltage, and the current detection circuit measures the generated current when the photodetector is exposed to electromagnetic radiation. The detection circuitry described herein can provide a bias voltage to the photodetector and can measure the photodetector's electronic response to ambient electromagnetic radiation. These three types are: whether or not a photovoltaic photovoltaic device has junction rectification as described below, and whether the device is operating with an externally applied voltage, also known as bias or bias voltage. And can be characterized. The photoconductor cell does not have a rectifying junction and operates with a normal bias. PV devices have at least one rectifying junction and operate without bias. The photodetector has at least one rectifying junction and is usually but not necessarily operated with a bias.

  Originally, photodetection optoelectronic devices are constructed of a plurality of inorganic semiconductors such as, for example, crystalline, polycrystalline, and amorphous silicon, gallium arsenide, cadmium telluride, and others. Here, the term “semiconductor” refers to a material that conducts electricity when charge carriers are introduced by thermal and electromagnetic excitation. The term “photoconductive” generally means that electromagnetic radiant energy is absorbed and thereby converted to the excitation energy of the electronic charge carrier so that the carrier can conduct, ie transport, the electronic charge in the material. It relates to processing. The terms “photoconductor” and “photoconductive material” are used herein to indicate a semiconductor material that is selected from the property of absorbing electromagnetic radiation and generating electronic charge carriers.

  More recently, optoelectronic devices using organic materials have been increasingly desired for various reasons. Since many materials used to make such devices are relatively inexpensive, organic optoelectronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as flexibility, are suitable for certain applications, such as making flexible substrates. Organic materials have the advantage of manufacturing processes compared to inorganic thin film technology that can make the organic material layer applicable to plastic substrates. Examples of organic optoelectronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells (OPVs), and organic photodetectors. As used herein, the term “organic” includes polymeric materials similar to small molecule organic materials that can be used to make organic optoelectronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecule groups may include repeat units in some situations. For example, the use of long chain alkyl groups as substituents does not remove molecules from the “small molecule” class. Small molecule groups can be incorporated into a polymer, for example, as a pendant group of a polymer backbone or as part of a polymer backbone. Small molecule groups can also serve as the core part of the dendrimer. Dendrimers consist of a series of chemical shells built into the core part.

  OLEDs use organic films that emit light when a voltage is applied to the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, lighting, and backlighting. For OLEDs, organic materials can have performance advantages over conventional materials. For example, the wavelength at which the organic emissive layer emits light can generally be easily adjusted using a suitable dopant. Some OLED materials and structures are described in US Pat. No. 5,844,363, US Pat. No. 6,303,238, and US Pat. No. 5,707,745, All of which are incorporated herein by reference.

  OLED devices are generally (but not necessarily) intended to emit light through at least one electrode, and one or more transparent electrodes are useful in organic optoelectronic devices. obtain. For example, a transparent electrode material such as indium tin oxide (ITO) can be used as the lower electrode. Transparent top electrodes, such as those disclosed in US Pat. No. 5,703,436 and US Pat. No. 5,707,745, which are hereby incorporated by reference in their entirety, are also described. Can be used. For an apparatus for emitting light only through the lower electrode, the upper electrode need not be transparent, but can be composed of a thick and reflective metal material having high electrical conductivity. Similarly, for devices for emitting light only through the upper electrode, the lower electrode may be opaque and / or reflective. If the electrode does not need to be transparent, the use of a thicker layer can provide good conductivity, and the use of a reflective electrode allows the light to be reflected towards the transparent electrode, The amount of light emitted through the other electrode can be increased. A completely transparent device can also be made in which both electrodes are transparent. Side-emitting OLEDs may also be made, and in such devices one or both electrodes may be opaque or reflective.

  As used herein, “upper” means the site furthest away from the substrate, while “lower” means the site closest to the substrate. For example, for a device having two electrodes, the bottom electrode is the electrode closest to the substrate and is generally the first electrode fabricated. The lower electrode has two surfaces, the bottom surface is closest to the substrate and the top surface is further away from the substrate. Where it is described that the first layer is “placed” or “deposited” on the second layer, the first layer is placed or deposited further away from the substrate. There may be other layers between the first and second layers, unless it is specified that the first layer is “in physical contact with” the second layer. For example, the cathode can be described as being “arranged on” the anode, even when various organic layers are present in between.

  As used herein, “solution processable” is dissolvable, dispersible, or transportable and / or precipitateable in a liquid medium, either in solution or suspension form. It means that there is.

US Pat. No. 5,844,363 US Pat. No. 6,303,238 US Pat. No. 5,707,745 US Pat. No. 5,703,436 US Pat. No. 5,707,745

  Solar cells can be characterized by the efficiency with which incident solar power can be converted into useful power. Devices that utilize crystalline or amorphous silicon occupy commercial applications, and some have achieved efficiencies of 23% or more of direct sunlight illumination. However, efficient crystal-based devices, particularly those with large surface areas, are difficult and expensive to manufacture due to the inherent problems in producing large crystals without significant efficiency loss defects. On the other hand, high efficiency amorphous silicon devices still suffer from stability problems. Current commercially available amorphous silicon cells have a stable efficiency of 4% to 8%. Due to manufacturing and stability issues associated with crystalline or amorphous silicon devices, the cost of power consumption generated per unit area is increasing. The current use of inorganic solar cells is currently limited by the high manufacturing costs for the power generated per unit area, as well as the annoying nature of the cell frame, the rest of the system equipment, and the high equipment costs resulting from the panel itself. Has been. Therefore, there is a need for a more economical method for producing PV cells with quantum yields that meet the requirements and thus have power conversion efficiency.

  More recent efforts have focused on the use of organic photovoltaic cells that can achieve photovoltaic conversion efficiency commensurate with conditions, as well as economic product costs. In organic materials, light absorption results in the formation of excitons, or constrained electron-hole pairs, rather than free electron-hole pairs generated in inorganic semiconductors. Exciton dissociation in organic materials is a donor-acceptor (DA) that is large enough that the difference in electron affinity and ionization potential between the contacting organic materials overcomes the exciton binding energy under strong electric fields. Occurs at the heterointerface. The latter mechanism is used to form organic DA planar heterojunction (HJ) photovoltaic cells with a power conversion efficiency of 0p-1%. This efficiency is limited by the light absorption length (LA to 1000 Å) exciton diffusion length (LD # 100 Å). When C60, which is LD to 400 angstroms, is used as an acceptor material (see US Pat. No. 6,580,027), power conversion efficiency of 0p to 3.6% has been demonstrated. Since excitons generated within the diffusion length of the excitons of the DA heterojunction receive the electric field of the junction, these excitons may have a high dissociation efficiency as a whole. Conversely, excitons generated outside the exciton diffusion length from the DA heterojunction can contribute to the device current with an overall low dissociation efficiency. Bulk heterojunctions fold many mutually in donor and acceptor materials to dissociate excitons generated by absorption of incident light to approach the heterojunction and efficiently contribute to the device current. Try to create a network that penetrates or interpenetrates.

  The present invention provides a method of manufacturing an organic optoelectronic device. Examples of organic optoelectronic devices made by the method of the present invention include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells (OPVs) (or solar cells), and organic photodetectors. However, it is not limited to these.

  According to an embodiment of the present invention, a method for manufacturing an organic optoelectronic device includes the following steps. Depositing a first layer having protrusions on the first electrode, wherein the first layer comprises a first organic small molecule material; such that the second layer is in physical contact with the first layer; Depositing a second layer on the first layer, wherein the minimum lateral dimension of the protrusion is between 1 and 5 times the exciton diffusion length of the first organic small molecule material; and Depositing a second electrode on the second layer to form an optoelectronic device. In another embodiment, the spacing between the protrusions is between 1 and 5 times the exciton diffusion length of the second layer.

  The present invention also provides a method of manufacturing an organic optoelectronic device having a bulk heterojunction.

  According to an embodiment of the present invention, a method for manufacturing an optoelectronic device includes the following steps. Depositing a first layer having a protrusion on the first electrode by organic vapor phase deposition, wherein the first layer comprises a small organic molecule material, and the minimum side dimension of the protrusion is the device Depositing a second layer over the first layer, wherein the first layer and the second layer, such that the second layer is in physical contact with the first layer; Is forming a bulk heterojunction; and depositing a second electrode on the second layer to form an optoelectronic device. For example, when the first layer is an electron donor layer, the first electrode is an anode, the second layer is an electron acceptor layer, and the second electrode is a cathode. As a further example, when the first layer is an electron acceptor layer, the first electrode is a cathode, the second layer is an electron donor layer, and the second electrode is an anode.

  According to another embodiment of the present invention, a method of manufacturing an optoelectronic device includes the following steps. Depositing a first layer having protrusions on the first electrode, wherein the first layer comprises a first organic small molecule material; such that the second layer is in physical contact with the first layer; Depositing a second layer on the first layer, wherein the interface of the second layer on the first layer forms a bulk heterojunction; and on the second layer to form an optoelectronic device. Depositing two electrodes. For example, when the first layer is an electron donor layer, the first electrode is an anode, the second layer is an electron acceptor layer, and the second electrode is a cathode. As a further example, when the first layer is an electron acceptor layer, the first electrode is a cathode, the second layer is an electron donor layer, and the second electrode is an anode.

  An object of the present invention is to provide a method of manufacturing an optoelectronic device including a bulk heterojunction. The method is continuous and is associated with so-called “roll-to-roll” manufacturing techniques, which results in optoelectronic devices having quantum yields and power conversion efficiencies commensurate with conditions.

FIG. 1 shows a schematic diagram of the following types of organic donor-acceptor photovoltaic cells. (A) bilayer cell; (b) bulk heterojunction cell; (c) mixed layer cell FIG. 2 shows a schematic diagram of organic vapor phase deposition (OVPD). OVPD occurs in a heated chamber and proceeds in three stages. Evaporation from the source cell, entrainment of organic vapor by the carrier gas towards the substrate, and diffusion across the boundary layer for absorption on the substrate. Hot chamber walls and directed gas flow increase deposition efficiency, prevent long term contamination and improve doping control. FIG. 3 shows a scanning electron micrograph of the following layers deposited by organic vapor phase deposition. (A) CuPc deposited on silicon at a lower substrate temperature of about 60 ° C .; (b) CuPc deposited on silicon at a lower substrate temperature of about 100 ° C .; (c) Lower substrate at about 100 ° C. CuPc deposited on ITO at temperature. FIG. 4 shows a schematic diagram of an optoelectronic device manufactured according to an embodiment of the method of the invention. FIG. 5 shows a scanning electron micrograph of the surface of a CuPc film having a continuous smear layer and needle-like crystals grown on a silicon wafer by OVPD. FIG. 6 shows a scanning electron micrograph of the surface of the CuPc film grown on indium tin oxide coated glass by OVPD. FIG. 7 shows a scanning electron micrograph of the surface of the CuPc film grown on indium tin oxide coated glass by OVPD. This inset is an atomic micrograph of the same sample. FIG. 8 shows a scanning electron micrograph of the surface of a 500-thick CuPc film grown on indium tin oxide coated glass by vacuum thermal evaporation. This inset is an atomic micrograph of the same sample. FIG. 9 (a) shows the Bragg-Brentano X-ray diffraction of CuPc film grown by OVPD on indium tin oxide coated glass. FIG. 9 (b) shows the Bragg-Brentano X-ray diffraction of the CuPc film grown by VTE on the indium tin oxide coated substrate. FIG. 10 shows a schematic diagram of the conformal surface and shadowing effect resulting from the free trajectory following the incident molecule in vacuum thermal evaporation. FIG. 11 shows a scanning electron micrograph of the surface of a PTCBI / BCP / Ag film grown by vacuum thermal evaporation on a CuPc needle tray. FIG. 12 shows a schematic diagram of the flat surface and gap filling properties in the top film grown in OVPD resulting from increasing surface diffusion of molecules and random arrival directions. FIG. 13 shows a scanning electron micrograph of the surface of the PTCBI layer grown on the CuPc needle. FIG. 14 shows the current-voltage characteristics of OVPD grown by controlling CuPc / PTCBI bulk heterojunction photovoltaic cells at various incident power levels. FIG. 15 shows power conversion efficiency ηp, open circuit voltage V _O c, filling ratio FF as a function of radiated power intensity P0 for OVPD grown by controlling a CuPc / PTCBI bulk heterojunction device.

  When suitable energy of electromagnetic radiation is incident on, for example, an organic molecular crystal (OMC) material or a semiconductor organic material such as a polymer, photons can be absorbed and generate an excited molecular state. This is symbolically represented by S0 + hνΨS0 *. Here, S0 and S0 * indicate a ground state and an excited state, respectively. This energy absorption is related to the propulsion of electrons from the ground state of HOMO, which can be a B-bond, to the LUMO, which can be a B * -bond, or similarly to the promotion of holes from the LUMO to the HOMO. . In the organic thin film photoelectric optoelectronic device, the generated molecular state is considered to be an exciton, that is, an electron-hole pair in a bound state transported as a quasiparticle. Excitons can have a significant lifetime before pair recombination. This pair recombination refers to the process in which the original electrons and holes recombine with each other, as opposed to recombining holes or electrons from other pairs. In order to generate a photocurrent, the electron-hole pairs must be separated, typically at the donor-acceptor interface between two dissimilar contact organic thin films. If the charges are not separated, they can recombine in a pair recombination process, also known as a quenching process, luminescent due to the emission of light of lower energy than incident light, or non-luminescent due to heat generation. . Neither of these results is desirable in a photoelectric optoelectronic device.

  Electric fields or inhomogeneities at the contacts can result in quenching rather than exciton separation at the donor-acceptor interface. As a result, no contribution is made to the current. It is therefore desirable to keep the photogenerated excitons away from the contact. This has the effect of limiting exciton diffusion to regions close to the junction to increase the chance that the associated electric field separates charge carriers released by exciton dissociation near the junction.

The usual way to generate electricity inside occupying a substantial volume is to juxtapose two layers of appropriately selected conductive materials, especially for the distribution of molecular quantum energy states. . The interface between these two materials is called a heterojunction photovoltaic cell. In the conventional semiconductor theory, the material for forming the PV heterojunction is generally shown as either n-type or p-type. Here, the n-type indicates that the main carrier type is an electron. This is seen in materials with many electrons that are in a relatively free energy state. The p-type indicates that the main carrier type is hole. Such materials have many holes in a relatively free energy state. The type of concentration of major carriers in the background, i.e. not photogenerated, mainly depends on unintentional doping by defects or impurities. The type and concentration of impurities determine the Fermi energy value, or level, in the gap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO), called the HOMO-LUMO gap. Fermi energy is characterized by a statistical occupation of molecular quantum energy levels indicated by an energy value with an occupation probability equal to 1/2. Fermi energy near the LUMO energy indicates that electrons are the dominant carrier. The Fermi energy near the HOMO energy indicates that holes are the dominant carrier. Therefore, Fermi energy is a major characteristic of conventional semiconductors, and a prototype PV heterojunction has a pn interface so far.

  The term “rectification” indicates, inter alia, that the interface has asymmetric conduction properties, ie that the interface favors charge transport in one direction. Rectification is usually associated with a built electric field that occurs between heterojunctions between appropriately selected materials.

  In the contents of organic materials, the terms “donor” and “acceptor” indicate only the relative positions of the HOMO and LUMO energies of two contacting but different organic materials. If the LUMO energy of one material in contact with another material is high (ie, the distance from the vacuum level is small), the material is a donor. A material is an acceptor if the HOMO energy of one material relative to the other material is low (same definition, but HOMO is measured directly with a lower ionization potential than the lower HOMO).

A significant characteristic of organic semiconductors is carrier mobility. Mobility measures the ease with which charge carriers can move through a conductive material that responds to an electric field. For free carrier concentration, carrier mobility is largely determined by the intrinsic properties of organic materials such as crystal symmetry and periodicity. Appropriate symmetry and periodicity can result in higher quantum wave function superposition in the HOMO level that results in higher hole mobility, or similarly LUMO level superposition resulting in higher electron mobility. Can occur. Furthermore, the donor or acceptor nature of, for example, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) organic semiconductors can help with higher carrier mobility. For example, chemical rationale suggests donor-type properties for PTCDA, and experiments show that hole mobility is a significant difference from electron mobility and that hole mobility is an important factor. Has been. The result is that device configuration expectations from donor / acceptor criteria are not verified by actual device performance. Rather than designating the electronic properties as “n-type” or “p-type”, depending on these unique electronic properties of the organic material, “hole transport layer” (HTL) or donor, or “electron transport layer” (ETL) or The term “acceptor” is frequently used. In this symbol display system, ETL is suitable for electron conduction, and HTL is suitable for hole conduction.

  A typical prior art photovoltaic device structure is an organic double layer battery, the schematic of which is shown in FIG. In double layer batteries, charge separation occurs primarily at organic heterojunctions. The built-in potential at the heterojunction is determined by the HOMO-LUMO energy difference between the two contact materials that form the heterojunction. The HOMO-LUMO gap correction between the donor and acceptor material creates an electric field at the donor / acceptor interface that facilitates charge separation for excitons generated within the exciton diffusion length at the donor / acceptor interface.

  The power conversion efficiency Op for both small molecular weight and polymer organic photovoltaic cells has steadily increased over the last decade. This advance relies on the introduction of a donor-acceptor (DA) heterojunction that serves as a dissociation site for photogenerated excitons that are strongly sold in large quantities. Further advances have been realized in polymer devices through the mixed use of donor and acceptor materials. Phase separation during spin coating results in a bulk heterojunction that removes the exciton diffusion barrier by forming an interpenetrating network of donor and acceptor materials. However, achieving a bulk heterojunction using a mixture of vacuum deposited small molecule materials results in significantly roughened film surfaces and shorted devices due to phase separation introduced by raising and lowering the substrate temperature. Have difficulty.

The external quantum efficiency of organic photoelectric optoelectronic devices is based on exciton separation at the DA interface, ie, O _EQE = O _A · O _ED · O _CC . Here, _{O A} is the absorption efficiency. The diffusion efficiency _OED is the fraction of photogenerated excitons that reach the DA interface before recombination. The carrier collection efficiency _OCC is the probability that free carriers generated at the DA interface due to exciton dissociation reach the corresponding electrode. Typically, in a double layer DA photovoltaic cell with an overall thickness L, on the order of the light absorption length LA, O _A = 1−exp (−L = L _A ) and O _CC when the optical interface effect is ignored. -100% is obtained. However, since the exciton diffusion length (L _D ) in organic materials is typically on the order of less than LA, the majority of photogenerated excitons remain unused for photocurrent generation ( FIG. 1 (a)). This _{is O EQE,} and therefore, the _{O P} of planar junction cell of this type, resulting in significant limitations. Conversely, when L is less than or equal to L _D , O _ED = 100%, so O _EQE is limited by O _A.

  In polymer photovoltaic cells, exciton diffusion barriers are eliminated by the introduction of bulk heterojunctions. A schematic diagram of the bulk heterojunction is shown in FIG. In a bulk heterojunction, the DA interface is folded in multiples so that photogenerated excitons are easy to find at the DA interface within a distance LD at the site of generation. So far, bulk heterojunction polymer photovoltaic cells in the art have a power conversion efficiency of around 3.5%.

Bulk heterojunction consists of (1) spin-coating a soluble kind of mixture of donor and acceptor materials, and (2) phase separation of the donor / acceptor material mixture by annealing a small molecular weight organic layer at high temperature. Is typically made. During spin coating and solvent evaporation, the donor and acceptor materials separate and create a complex interpenetrating network with a large interfacial area between the two phases. The morphology of the generated structure is controlled by changing the spin state, solvent, and relative material concentration. The challenge of these systems is to balance a high O _ED suitable for fine particle form with a high O _CC suitable for coarse particle size so that the yield O _ED · O _CC is maximized. The method of phase separation induced by annealing is described in “Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films” in Nature 425 (2003) 158-162 by Peumans, Uchida & Forrest.

At present, the realization of bulk heterojunctions in small molecule systems has generally not been successful. Attempts to achieve valve heterojunction via co-deposition of donor and acceptor materials have resulted in lower power conversion efficiency than can be used in optimal double layer devices using the same material. Strong quenching of photoluminescence in the mixed material indicates O _ED ˜100%. Therefore, low efficiency is caused by poor charge transport, resulting in low carrier collection efficiency Occ (see FIG. 1 (c)). If charge collection is facilitated by application of an external voltage, a stiff external quantum efficiency can be obtained.

  Growth of the mixed layer at an elevated substrate temperature results in phase separation and the appearance of crystalline regions. However, this increases crystallinity, with larger LDs at the expense of increased film roughness. The high density pinholes that cause a short circuit between the cathode and anode contacts in such a structure make device fabrication impractical. A similar problem occurs when the mixed layer is annealed after deposition to introduce phase separation.

  Furthermore, even though the bulk heterojunctions produced by the above-described method result in increased power conversion efficiency, these bulk heterojunctions exhibit high series resistance due to the irregular structure of the interface layer. Phase separation during spin coating of the polymer, and phase separation induced by annealing, are both characterized by randomly building interdigitation between the donor and acceptor layers due to the entropy of the interface formation process. "Dynamic driving" method.

  In accordance with the present invention, a method is provided for making an organic optoelectronic device having a bulk heterojunction in a small molecule system. More specifically, the method also provides a method for controlling the growth of regular bulk heterojunctions. According to an embodiment of the invention, a first layer comprising an organic small molecule material is deposited across the first electrode by organic vapor phase deposition (OVPD). This method is believed to produce a bulk heterojunction with a high surface-volume ratio and suppressed series resistance compared to other known methods. As shown in Table 1 and described further below, ηp for a device having a bulk heterojunction made by OVPD according to embodiments of the present invention is obtained using an equivalent planar heterojunction PV cell. It was approximately 2.5 times larger than the one and 1.9 times larger than the annealed and thermodynamically orbited bulk heterojunction. Thus, it is believed that controlled growth in the preferred embodiment of the CuPc / PTCBI bulk heterojunction provides the desired increase in junction surface area without resulting in an increase in cell series resistance.

  Typically, thin films of organic optoelectronic devices such as OLEDs and OPVs are grown by thermal evaporation in high vacuum, allowing the high purity and structural control necessary for reliable and efficient operation (SRForrest, Chem. Rev. 97, 1793 (1997)). However, controlling film thickness uniformity and dopant concentration over the large area required for the product can be difficult using vacuum deposition (S. Wolf and RN Tauber, Silicon Processing for the VLSI Era (Lattice, 1986)). In addition, a significant percentage of the vapor covers the cold walls of the deposition chamber. Over time, inefficient use of materials can result in thick films that can be peeled off, resulting in particle contamination of the system and substrate. The potential throughput of vacuum deposited organic thin film devices is low, resulting in high product costs. Low pressure organic vapor phase deposition (LP-OVPD) is a vacuum in that OVPD can be applied to the deposition of dopants in a deposited film to apply organics on large area substrates for rapid, particle-free, uniform deposition. Recently demonstrated as an excellent alternative to thermal evaporation (VTE) (MA Baldo, M. Deutsch, PE Burrows, H. Gossenberger, M. Gerstenberg, VS Ban, and SR Forrest, Adv. Mater 10, 1505 ( 1998)).

OVPD is a widely used vacuum thermal evaporation (VTE) in that it uses a carrier gas in the deposition chamber to transport organic vapor, where molecules diffuse across the boundary layer and physisorb onto the substrate. Is essentially different. This film deposition method is most similar to the hydrogenated gas phase epitaxy used in III-V semiconductor growth (GB Stringfellow, Organometallic Vapor-Phase Epitaxy (Academic, London, 1989); GH Olsen Written in GaInAsP, edited by TP Pearsall (Wiley, New York, 1982). In LP-OVPD, organic compounds are thermally evaporated and transported through a hot wall gas carrier tube into the deposition chamber by an inert carrier gas against a cooling substrate where condensation occurs. The flow pattern can be designed to obtain a substrate selection, uniform distribution of organic material, resulting in a very uniform film thickness and minimization of material consumption.

  Virtually all organic materials used in thin film optoelectronic devices have a sufficiently high vapor pressure that evaporates at temperatures below 400 ° C. and is transported into the vapor phase by a carrier gas such as argon or nitrogen. ing. This makes it possible to place the evaporation source outside the reactor tube (as in the case of metal organic chemical vapor deposition), spatially separating the evaporation and transport functions and providing precise control of the deposition process (See S. Wolf and RN Tauber, Silicon Processing for the VLSI Era (Lattice, 1986); GB Stringfellow, Organometallic Vapor-Phase Epitaxy (Academic, London, 1989)))).

The concept of OVPD is illustrated in FIG. Vapor species A is generated by heating the feed material in a stream of inert carrier gas, which transports the vapor into the deposition chamber. The gas flow around the substrate forms a velocity boundary layer in which molecules (typically <0.01%) are diffused and adsorbed onto the substrate. This process can be analyzed as a series of different transport stages. Along with the dynamics of organic species A adsorption on the substrate, these steps are summarized below.
Steam: Formula (1a)
Recondensation: Formula (1b) below
Entrainment by carrier gas: Formula (1c) below
Transport to substrate: Formula (2) below
Diffusion across the boundary layer to the substrate: (3a)

Desorption from substrate to vapor phase: Formula (3b) below
Surface diffusion and immobilization: Formula (3c) below
Here, As represents a solid or liquid organic molecular species, and k is a rate constant representing the characteristic speed of the corresponding process. For example, the species As and Ag evaporate and recondense inside the feed cell at characteristic speeds kevap and kcond, respectively. This classification shows the overall efficiency of the process in addition to establishing the speed limit stage. For example, evaporation occurs either in the so-called “dynamic” type, where kevap> kcond, or in the equilibrium type, where kevap = kcond. Organic species are swept from the supply cell in reaction (1c) by the carrier gas. Entrainment by carriers causes Acg to be taken around the substrate at a specific bulk transport rate kt, resulting in an Acg, subs of 100% overall efficiency in this region, while the remainder is pushed out of the deposition chamber. Deposition occurs by diffusion of A across the boundary layer and by adsorption at a characteristic rate kads. The overall deposition rate is rdep = kdep−kdes, where kdes is the desorption rate from the substrate. In the source vessel, the net organic vapor efflux rate is represented by mass balance, where the difference between the evaporation rate kevap and the recondensation rate kcond gives the rate at which the organic vapor is removed from the source cell.

  US Pat. No. 6,337,102 describes the basis for organic vapor phase deposition, which is incorporated herein by reference in its entirety. In addition, co-pending U.S. Patent Application Publication No. 2004/0048000 is hereby incorporated by reference in its entirety. This co-pending US patent application describes an apparatus and method for depositing an organic vapor stream that can be used by the method of the present invention.

The organic vapor phase deposition described in US Pat. No. 6,337,102 is characterized in that the resulting thin film is characterized by superior surface properties such as “low surface roughness” (US Pat. No. 6,337,102). In the present specification, the organic vapor phase deposition preferably uses a state in which island-like growth occurs in addition to the Stranski-Krastanov layer. (See SR Forrest, Chem. Rev. 97, 1793 (1997)). That is, the organic vapor deposition in the present invention involves a sufficiently high substrate temperature and deposition to generate cohesive energy of the organic small molecule material so that it adsorbs to the material itself rather than the substrate in which the organic small molecule material resides. It is preferred to use chamber pressure. This growth type facilitates the deposition of a first layer comprising an organic small molecule material having a sufficiently high surface area-volume ratio to form a bulk heterojunction bottom layer. Preferably, the deposited first layer has a surface area to volume ratio of at least 2: 1, more preferably at least 5: 1. These surface area and volume measurements are preferred techniques for, for example, atomic force microscope (AFM), scanning electron microscope (SEM), or cross-sectional transmission electron microscope (TEM) (fully fabricated optoelectronic devices). Can be made by microscopic techniques known in the art. This increase in surface area-volume ratio increases the exciton dissociation probability and thereby the efficiency of the fabricated optoelectronic device. As the term “surface area-volume ratio” is used herein, the term “surface area” does not indicate the total surface area of the deposited first layer, but the second layer deposited thereon. Only the surface area of the deposited first layer in contact with the layer (ie, the interface between the first layer and the second layer) is shown.

  The temperature and pressure used during organic vapor phase deposition depends inter alia on the organic material used. For example, when depositing a first layer comprising copper phthalocyanine (CuPc) as an electron donor layer on the first electrode, a preferred deposition chamber pressure is in the range of about 50 mTorr to about 10 mTorr, and a preferred source cell temperature is about The preferred inherent substrate temperature is in the range of about 0 ° C. to about 100 ° C., which ranges from 370 ° C. to about 470 ° C. More preferably, the deposition chamber pressure ranges from 0.15 Torr to 0.80 Torr, the preferred source cell evaporation temperature is at least 400 ° C., and the underlying substrate temperature is less than 40 ° C. The underlying substrate is the substrate that is intrinsic to all deposited layers, and in fact, the substrate temperature is the temperature of the underlying substrate being controlled during OVPD. However, since the layers deposited on the substrates are all relatively thin, the temperature of these layers is such that the temperature of the material on which the first layer is deposited by OPVD is approximately equal to the temperature of the underlying substrate. Is approximately equal to the temperature of the underlying substrate. In addition, the flow rate of the nitrogen gas carrier is preferably in the range of 10 sccm to 200 sccm.

  The use of organic vapor phase deposition to form bulk heterojunctions during the fabrication of optoelectronic devices provides advantages over conventional methods of forming bulk heterojunctions. For example, OVPD does not require post-deposition annealing to the fabricated device, and allows for the direct deposition of separate layers to form heterojunctions on various substrates including plastic layers. Usually, plastic substrates cannot be exposed to the high temperatures required for post-deposition annealing. Thus, the use of OVPD not only potentially reduces the cost of fabricating optoelectronic devices with bulk heterojunctions by eliminating the need for post-deposition annealing, but also allows for a wide range of substrates (ie, plastic substrates). It can be used in connection with such fabrication.

  According to another embodiment of the method of the present invention, a first layer having protrusions is deposited on a first electrode, the first layer comprising a first organic small molecule material. According to this embodiment, the first layer is formed via methods known in the art such as vacuum deposition, vacuum thermal evaporation, spin coating, organic vapor phase deposition, ink jet printing, and other known methods. Can be deposited. It is preferable to use a state in which island-like growth occurs in addition to the Stranski-Krastanov layer (see S. R. Forrest, Chem. Rev. 97, 1793 (1997)). That is, the deposition of the first layer having the protruding portion uses a state in which the cohesive energy of the first organic small molecule material is generated so that the organic small molecule material is adsorbed to the material itself rather than the underlying substrate. preferable. This growth type facilitates the deposition of a first layer comprising a first organic small molecule material having a sufficiently high surface area-volume ratio to form a bulk heterojunction bottom layer. The surface area-volume ratio in the deposited first layer is preferably at least 2: 1 and more preferably at least 5: 1. By increasing this surface area-volume ratio, the exciton dissociation probability and thereby the efficiency of the fabricated optoelectronic device is increased.

Preferably, the diameter of each protrusion in the deposited first layer is greater than or equal to the exciton diffusion length (LD1) of the first organic small molecule material constituting the first layer. More preferably, the diameter of each protrusion in the deposited first layer is in the range of about 1 to about 5 times the exciton diffusion length (LD1) of the first organic small molecule material. More preferably, the diameter of each protrusion in the deposited first layer is in the range of about 1.5 to about 3 times the exciton diffusion length (LD1) of the first organic small molecule material. These diameter measurements can be determined by microscopy techniques known in the art, such as, for example, AFM, SEM, or cross-sectional TEM (which is the preferred technique for fully fabricated optoelectronic devices). By depositing the first layer with such a diameter protrusion, the DA interface is such that the photogenerated excitons of the first layer can easily find the DA interface within the distance LD1 of the generation site. Should be molded. Similarly, the second layer deposited thereon is preferably similarly shaped. In other words, the protrusions of the deposited first layer have a space where the space between these protrusions has a diameter equal to or greater than the exciton diffusion length (LD2) of the second organic small molecule material having the second layer. It is uniformly arranged so as to correspond to the two opposite protrusions. More preferably, the diameter of each protrusion in the deposited second layer ranges from about 1 to about 5 times the exciton diffusion length (LD2) of the second organic small molecule material. More preferably, the diameter of each protrusion in the deposited second layer ranges from about 1.5 times to about 3 times the exciton diffusion length (LD2) of the second organic small molecule material. As used herein, the space between these protrusions has the shortest lateral distance between two adjacent protrusions. By depositing the first layer with such uniformly arranged protrusions, the DA interface is found at the DA interface where the photogenerated excitons of the second layer are within the distance LD2 of the production site. Molded for ease. Preferably, the height of the protrusion is at least equal to at least half the diameter of the protrusion. As used herein, the term “diameter” is described as a measure of a certain appearance size of the protrusion, and does not limit the protrusion to a circular or cylindrical shape. This is because the protrusion can take various shapes. As used herein, the term “diameter” refers to the smallest lateral dimension of appearance, ie, the smallest dimension in a direction parallel to the plane of the substrate on which the device is fabricated. At any point in the protrusion, the excitons are present at a length greater than 2.5 exciton diffusion length from the interface, more preferably at a distance greater than 1.5 diffusion length from the interface (preferred diameter range is 1-5 And 1.5-3 diffusion length). Consistent with the idea of controlling the maximum distance that excitons must travel to reach the interface, the profile of the side protrusion is not necessarily constant as a function of the distance in the direction perpendicular to the side, It will be appreciated that the “minimum side dimension” or “diameter” of an outline is measured at a side cross section that can reasonably reveal the overall outline, as opposed to, for example, at the tip.

  Organic thin film crystal size and morphology may be controllable in OVPD. Although uncontrollable growth, believed to be due to excessive deformation, is believed to lead to short circuit defects in the PV cell, it is preferable to control the growth of the protrusions of the first deposited layer in the PV device. In a preferred embodiment, the diameter of the first layer protrusion is less than 5% of the thickness of the device. More preferably, the diameter is less than 10% of the thickness of the device. As described herein, the growth of protrusions can be controlled by selection of OVPD process parameters. Related parameters may include the underlying substrate temperature, source evaporation temperature, nitrogen gas carrier flow rate, chamber pressure. The underlying substrate temperature is thought to control the growth of the needles or protrusions, selected to promote sufficiently to adsorb the evaporated organic material to the substrate, and to support a relatively high nucleation density Is done. The source evaporation temperature is bounded by the vapor pressure of the organic material and its upper limit due to its thermal chemical stability (typically over 400 ° C. for most organic materials used in thin film devices) , Determined by the desired deposition rate. It is further believed that a 10 sccm-200 sccm nitrogen gas carrier flow rate results in an optimal boundary layer thickness at the donor / acceptor interface that facilitates transport of organic material. The chamber pressure is globally limited by the pump used in the OVPD system and also depends on the gas carrier flow rate. As shown in FIG. 12, the preferred range of 0.15 Torr-0.80 Torr is believed to facilitate the filling of the gap by the acceptor material and the recesses of the underlying donor film. Based on the materials used and the desired results, parameters outside these ranges can be used in certain situations.

  According to the method of the embodiment of the present invention, after the first layer containing the first organic small molecule material is deposited on the first electrode, the second layer is in physical contact with the first layer. As such, the interface of the second layer on the first layer and the second layer forms a bulk heterojunction on the first layer. The second layer can be deposited via vacuum deposition, vacuum thermal evaporation, spin coating, organic vapor phase deposition, ink jet printing, or other methods known in the art. Preferably, the upper surface of the upper organic layer can be a second layer, but is relatively flat so that a short circuit to current is prevented. It is believed that deposition by OVPD at selected process parameters promotes planarization of the top film surface by other deposition techniques such as VTE. In VTE, the deposited film typically has a morphology that conforms to the underlying surface resulting from the free trajectory following the incident molecule (see FIG. 10). Thus, the acceptor material surface results in a second, highly folded needle array following that of the donor material needle. In addition, the vacancy tends to grow in regions where the protrusions block the underlying film surface from the acceptor material source cell. This is also shown in FIG. 11, where the VTE grown PTCBI / BCP / Ag layer shows a dense void at the base of the highest CuPc needle. On the other hand, surface diffusion with an irregular direction of arrival such that the molecules cross the boundary layer at the substrate surface of OVPD growth, as shown in FIGS. 12 and 13, the space below the underlying CuPc needle. This is believed to result in a planarized upper film surface that is completely filled.

  When the first layer is deposited by OVPD, the second layer is also preferably deposited on the first layer by OVPD. As can be appreciated by those skilled in the art, the temperature and pressure used during the second layer of OVPD is based on the organic material used. For example, a second layer containing 3,4,9,10-perylenetetracarboxylic acid-bis-benzimidazole (PTCBI) as an electron acceptor layer (by OVPD) a first layer containing copper phthalocyanine (CuPc) as a first donor layer When deposited on, a suitable deposition chamber ranges from about 50 mTorr to about 10 mTorr, a suitable source cell temperature ranges from about 370 ° C. to about 470 ° C., and a suitable underlying substrate temperature is The range is from about 0 ° C to about 100 ° C. More preferably, the deposition chamber process ranges from 0.15 Torr to 0.80 Torr, the preferred source cell evaporation temperature is at least 400 ° C., and the underlying substrate temperature is less than 40 ° C. Since these suitable temperature and pressure ranges are the same as those used to deposit the first layer comprising CuPc as the electron donor layer on the first electrode described above, the OVPD process is performed in the same deposition chamber. Which helps to speed up and streamline the manufacturing process.

  Although any thickness layer may be used by the method of the present invention, some guidelines should be considered in selecting a suitable layer thickness when manufacturing an optoelectronic device according to the method of the present invention. The exciton diffusion length LD is preferably equal to or greater than the layer thickness L. This is because most exciton dissociation is considered to occur at the interface. When LD is less than L, many excitons can be recombined before dissociation. The total photoconductive layer thickness is on the order of electromagnetic radiation absorption length, 1 / ∀ (where ∀ is the absorption coefficient), but most of the radiation incident on the solar cell is absorbed and excitons Is preferable. Furthermore, the thickness of the photoconductive layer should be as thin as possible to avoid excessive series resistance due to the high bulk resistance of organic semiconductors.

  Therefore, these competing guidelines inherently require a compromise that is made in selecting the thickness of the photoconductive organic layer of the photoelectric optoelectronic device. Thus, on the one hand, it is desirable that the thickness be equal to or greater than the absorption length (for a single cell device) in order to absorb the maximum amount of incident light. On the other hand, as the photoconductive layer thickness increases, two undesirable effects increase. One is that due to the high series resistance of organic semiconductors, increased organic material thickness increases device resistance and reduces efficiency. Another undesirable effect is that increasing the thickness of the photoconductive layer increases the likelihood that excitons will be generated away from the effective region of the charge separation interface, thereby increasing the probability of pair recombination and Again, this leads to a reduction in efficiency. Therefore, it is desirable for the device configuration to balance these competing effects in a way that produces high quantum efficiency for the entire device. For example, by using multiple stacked subcells, the photoconductive organic layer can be made very thin. In summary, by taking into account the above-mentioned competing effects, namely the absorption length of the photoconductive material in the device, the diffusion length of these materials, the photocurrent generation efficiency of these excitons, and the resistance of these materials. The rate, layer thickness in the device, can be adjusted to obtain the maximum internal quantum efficiency (and parameters directly related thereto) for a particular material for the required set of ambient radiation conditions.

  As described above, the interface of the second layer on the first layer forms a bulk heterojunction that generates an electric field therein. Preferably, the bulk heterojunction is formed by an electron donor layer that is in physical contact with the electron acceptor layer. The material comprising the electron donor layer has a lower ionization potential than the material comprising the electron acceptor layer. Furthermore, the HOMO / LUMO gap of the ionization potential of the electron donor layer must be smaller than that of the electron acceptor layer. Overall, materials with electron donor layers or electron acceptor layers should have the longest possible exciton diffusion length, and therefore these are useful for the regular deposition of molecules, such as planar aromatic molecules. These materials are preferred.

  The electron acceptor layer can be composed of, for example, perylene, naphthalene, fullerene, or a nanotube. A suitable electron acceptor material is 3,4,9,10-perylenetetracarboxylic acid-bis-benzimidazole (PTCBI). Alternatively, the electron acceptor layer is made of a fullerene material, such as Buckminsterfullerene (C60), as described in US Pat. No. 6,580,027, which is incorporated herein by reference in its entirety. It may be configured.

  The electron donor layer may be made of, for example, phthalocyanine, polyolefin, a derivative, or a transition metal compound thereof. A preferred electron donor material is copper phthalocyanine (CuPc).

  According to an embodiment of the method of the invention, the second electrode is deposited on the second layer to form an optoelectronic device. The second electrode can be deposited via methods in the art such as, for example, vacuum deposition and spin coating. The electrodes or contacts used in photoelectric optoelectronic devices are important considerations as shown in US Pat. No. 6,352,777, which is incorporated herein by reference in its entirety. Material. As used herein, “electrode” and “contact” are layers that provide a medium for transporting photogenerated power to an external circuit or for providing a bias voltage to the device. Indicates. That is, the electrode or contact is the photoconductive active region of the organic photoelectric optoelectronic device and other means for transporting wires, leads, traces, or charge carriers to or from the external circuit. Provides an interface between In a photoelectric optoelectronic device, it is desirable to be able to maximize the amount of ambient electromagnetic radiation from the device to the outside allowed in the photoconductive active internal region. That is, the electromagnetic radiation must reach a photoconductive layer where the light can be converted to electricity by photoelectric absorption. This often dictates that at least one of the electrical contacts should absorb and reflect minimally incident electromagnetic radiation. That is, such a contact should be substantially transparent. The opposing electrode may be a reflective material such that light that passes through the cell without being absorbed reflects the cell. As used herein, a layer of material or a series of multiples in different materials when the layer or layers allow transmission of at least 50% ambient electromagnetic radiation at the relevant wavelength. The layer is said to be “permeable”. Similarly, a layer that allows some but less than 50% transmission of ambient electromagnetic radiation at the relevant wavelength is said to be "semi-transmissive".

  The electrode is preferably composed of a metal or “metal substitute”. In the present specification, the term “metal” includes a material composed of a basic pure metal such as Mg and two or more basic pure metals including both Mg and Ag and expressed as Mg: Ag. It is used to include any of metal alloys made of metal. Here, the term “metal substitute” refers to a material that is not a metal in the official definition, but has the same properties as a metal desired in a given suitable application. Examples of metal substitutes commonly used for the electrode and the charge transport layer include transparent conductive materials such as indium tin oxide (ITO), gallium indium tin oxide (GITO), and zinc indium tin oxide (ZITO). And doped wide band gap semiconductors such as conductive oxides. In particular, ITO is a heavily doped semiconductor modified to n + with an optical band gap of approximately 3.2 eV that transmits wavelengths greater than approximately 3900 nm. Other suitable metal substitutes include transparent conducting polymer polyanaline (PANI) and its chemical related. The metal substitute can be further selected from a wide range of non-metallic materials. Here, the term “non-metallic” is meant to include a wide range of materials provided in metal-free materials in a chemically unbonded form. When a metal is present in a non-chemically bonded form, either alone or bonded as an alloy with one or more other metals, the metal is in metallic form. Alternatively referred to as present or present as "free metal". Accordingly, the metal surrogate electrode in the present invention can sometimes be referred to as being “metal free”. Here, the term “metal free” means to explicitly include a metal free material in a chemically unbonded form. Free metals typically have a form of metal bonding that arises from a sea of valence electrons that can move freely through a metal lattice in the electron conduction band. Metal substitutes may contain metal constituents, but these are “non-metallic” in some bases. These are not pure free metals and are not alloys of free metals. When the metal is present in its metallic form, the electronic conduction band tends to provide high conductivity with high reflectivity for optical radiation among other metal properties.

  Embodiments of the method of the present invention include US Pat. No. 6,469,437, US Pat. No. 6,469,437 by Parthasarathy et al. (“Parthasarathy”), one or more transparent electrodes in the fabricated optoelectronic device. A highly permeable, non-metallic, low resistance cathode, as described in US Pat. No. 6,420,031, or US Pat. No. 5,703,436 by Forrest et al. (“Forrest”). Included are high efficiency, low resistance metal / non-metallic compound cathodes as described in the specification and US Pat. No. 6,297,495. Each type of cathode is an organic material such as copper phthalocyanine (CuPc) to form a highly permeable, non-metallic, low resistance cathode or to form a highly efficient, low resistance metal / non-metallic compound cathode. A thin Mg: Ag layer is suitably prepared in a manufacturing process that includes sputter depositing an ITO layer on either. Parthasarathy discloses an upper ITO layer on which an organic layer is deposited instead of an upper organic layer on which an ITO layer that does not function as an efficient cathode is deposited.

  Here, the term “cathode” is used in the manner described below. In a non-stacked photoelectric optoelectronic device or in a single unit of a stacked photoelectric optoelectronic device connected to a resistive load and without externally applied voltage, e.g. solar cells, etc. , Move from the adjacent photoconductive material to the cathode. Similarly, the term “anode” is used herein so that holes move from an adjacent photoconductive material to the anode in an illuminated solar cell. This is equivalent to an electron moving in the opposite direction. It should be noted that as used herein, the anode and cathode may be electrodes or charge transport layers.

  In other embodiments of the present invention, the optoelectronic device can be fabricated on a substrate. For example, the first electrode may be on the substrate such that when the first layer is deposited on the first electrode, the first layer is also deposited on the substrate. The substrate may be any suitable substrate with the desired structural characteristics. The substrate may be flexible or rigid and may be transmissive, translucent, or impermeable. Plastic and glass are examples of suitable rigid substrate materials. Plastic and metal foils are examples of suitable flexible substrate materials. The substrate may be a semiconductor material for facilitating circuit fabrication. For example, the substrate may be a silicon wafer on which circuits are made that can control optoelectronic devices subsequently deposited on the substrate. Other substrates can also be used. The material and thickness of the substrate can be used to obtain the desired structural and optical properties.

  In a further embodiment of the present invention, a method of manufacturing an optoelectronic device is described in US Pat. No. 6,097,147 and US Pat. No. 6,451,415, which are hereby incorporated by reference in their entirety. May include one or more exciton blocking layers (EBLs) as described in Applied Physics Letters 2000, 76, 2650-52. The EBL can be deposited via methods known in the art such as vacuum deposition, vacuum thermal evaporation, spin coating, organic vapor phase deposition, ink jet printing, and other known methods. Higher internal and external quantum efficiencies contain one or more EBLs that confine photogenerated excitons in the region near the dissociation interface and prevent quenching of the plastic excitons at the photosensitive organic / electrode interface Is achieved by In addition to limiting the volume that excitons can diffuse, EBL can act as a diffusion barrier to materials introduced during electrode deposition. In some situations, the EBL can be made thick enough to compensate for pinholes or short-circuit defects that can render the organic PV device non-functional. Therefore, EBL helps to protect the fragile organic layer from damage that can occur when the electrode is deposited on the organic material.

  EBLs are believed to have exciton blocking properties by having a substantially high LUMO-HOMO energy gap from adjacent organic semiconductors where excitons are blocked. Thus, confined excitons are prohibited from flowing out of the EBL due to energetics considerations. While it is desirable for EBLs to block excitons, it is not desirable for EBL to block all charges. However, due to the nature of adjacent energy levels, an EBL necessarily blocks only one sign of charge carrier. By design, EBL always exists between two layers, usually an organic light-sensitive semiconductor layer and an electrode or charge transport layer. An adjacent electrode or charge transport layer is either a cathode or an anode herein. Therefore, the material for the EBL at a given location in the device is selected such that the desired sign carrier is prevented from transporting to the electrode or charge transport layer. Appropriate energy level placement ensures that there is no barrier to charge transport and prevents an increase in series resistance. For example, for materials used as cathode-side EBL, adjust the LUMO level to be close to the LUMO level of the adjacent acceptor material so that any undesirable barrier to electrons is minimized. Is desirable.

  It should be understood that the exciton blocking property of a material is not an intrinsic property. Whether a given material acts as an exciton blocker is based on the relative HOMO and LUMO levels of adjacent organic photoelectric materials. Therefore, it is not possible to identify the type of compound by separating it as an exciton blocking material without considering the contents of the device used. However, those skilled in the art, using the teachings herein, will determine whether a given material functions as an exciton blocking layer when used with a selected set of materials for constructing an organic PV layer. Can be identified.

  In a preferred embodiment of the present invention, the EBL is deposited between the electron acceptor layer and the cathode. Suitable materials for EBL include 2,9-dimethyl-1,10-phenanthroline (also referred to as bathocuproin or BCP), which is believed to have a LUMO-HOMO separation of about 3.5 eV, or Bis (2-methyl-8-hydroxyquinolinolato) -aluminum (III) phenolate (Alq2OPH). BCP is an effective exciton blocking material that can easily transport electrons from the adjacent electron acceptor layer to the cathode. Further, when BCP is deposited by OVPD, a suitable source temperature for BCP is in the range of about 150 ° C to about 250 ° C.

  Embodiments of the method in the present invention may include a translucent deposit for transport to the charge transport layer. As indicated herein, the charge transport layer is often, but not necessarily, an inorganic material and is selected to be totally photoconductive and not active, thereby providing a charge transport layer. Is distinguished from a donor layer and an acceptor layer. As used herein, the term “charge transport layer” is similar to an electrode, but differs in that the charge transport layer transports only charge carriers from one subsection of an optoelectronic device to an adjacent subsection. Indicates the layer.

  In a further embodiment of the method in the present invention, one or more deposited layers may be treated with a plasma before depositing the next layer. These layers may be treated with, for example, a weak argon or oxygen plasma. This treatment is beneficial because it reduces the series resistance.

  In another embodiment of the method according to the present invention, the paint layer is deposited on the first electrode such that the first layer is deposited on the paint layer (ie, the paint layer is the first electrode and the first electrode). And the planarization layer is deposited on the second layer such that the second electrode is deposited on the planarization layer (ie, the planarization layer is the second layer and Between the second electrodes). The deposition of the wetting layer and the planarization layer makes it easier to prevent the formation of pinholes in the thin film of the produced optoelectronic device. When depositing the second electrode on top of the previously deposited layer, an electrical short can occur due to the penetration of the second electrode into the pinhole and contact with the underlying first electrode. However, the occurrence of such an electrical short circuit is easily prevented by the deposition of the wetting layer and the planarization layer. A typical material for the planarization and paint layers is a 3,4-polyethylenedioxythiophene: polystyrene sulfonate (PEDOT: PSS) film.

  According to this embodiment of the invention, the wetting layer and planarization layer are used in the industry such as vacuum deposition, vacuum thermal evaporation, spin coating, organic vapor phase deposition, ink jet printing, and other known methods. It can be deposited by a method. When using OVPD to deposit paint and planarization layers, lower substrate temperatures and deposition chamber pressures used for the deposition of the first layer may be used.

  Overall, due to the high bulk resistivity of organic photoconductors, it is desirable to use relatively thin films of these materials when making organic optoelectronic devices. However, since the thin photosensitive layer absorbs a smaller proportion of incident light, the external quantum efficiency of the thin photoconductor can be lower than that of the thick photoconductor. However, the external quantum efficiency in thin layer organic devices as described herein can be further increased by a suitable design of the device structure. Device structures that provide a means to increase the effective thickness of the absorber layer with the thin photoactive layer described herein may be suitable. One such configuration is a stacked device as described in US Pat. No. 6,657,378, which is incorporated herein by reference in its entirety. It should be understood that the method of the present invention can be used in the manufacture of stacked optoelectronic devices, such as those described in US Pat. No. 6,657,378. As used herein, the terms “laminated”, “laminated”, “multi-section”, “multi-cell” refer to a photosensitive material separated by one or more electrodes or charge transport layers. 1 shows an optional optoelectronic device having a plurality of layers. When the term “subcell” is used herein, it refers to the structure of an organic photoelectric optoelectronic device. When a subcell is used individually as a photoelectric optoelectronic device, it typically includes a set of electrodes, namely a positive electrode and a negative electrode. In a deposited optoelectronic device, the corner subcells in the device may be electrically connected either in parallel or in series based on whether the current and / or voltage generated by the device is maximized. Good. In some stacked arrangements, adjacent subcells can be used in common, i.e., with a shared electrode or charge transport layer. In other cases, adjacent subcells do not share a common electrode or charge transport layer, but are instead separated by an electron-hole recombination region comprising, for example, metal nanoclusters, nanoparticles, or nanorods. Thus, a subcell may include a subunit structure regardless of whether each subunit has a unique electrode or shares an electrode or charge transport layer with an adjacent subunit. Here, the terms “cell”, “subcell”, “unit”, “subunit”, “section”, and “subsection” refer to a photoconductive layer or set of layers and an adjacent electrode or charge transport layer. Used interchangeably.

  As noted above, in some embodiments in a stacked structure, as disclosed in US Pat. No. 6,657,358, which is hereby incorporated by reference in its entirety, The individual subcells in the fabricated device are separated by an electron-hole recombination region. As used herein, “front” means the part closest to the incident electromagnetic light and “back” means the part farther from the electromagnetic radiation source. The electron-hole recombination region contributes to preventing the formation of an inverted heterojunction between the exciton blocking layer in the front cell and the donor layer in the back cell. It will be appreciated that any number of subcells may be combined in this manner. If photoinduced current is achieved in a stacked device, effective recombination of electrons from the front subcell and holes from the back subcell is necessary. The electron-hole recombination region preferably comprises a thin metal layer. This metal is translucent to allow light to reach the back cell. For this purpose, it is preferred that the metal layer be less than about 20Δ thickness. It is particularly preferred that the metal film is about 5Δ thick. These ultrathin metal films (˜5Δ) are not continuous thin films, but rather are composed of spaced metal nanoparticles, nanorods, or nanoclusters. Surprisingly, the ultrathin metal layer is not continuous, but still provides an effective layer for electron-hole recombination. Suitable materials for use in this layer include Ag, Li, LiF, Al, Ti and Sn. Silver is a particularly preferred metal for this layer. Gold is not considered a good choice for this layer because it is not known to introduce a midgap state. In one embodiment in the deposited device, the electron-hole recombination region includes electrically active defects that result in rapid electron-hole recombination. This defect can be introduced by limited damage at this interface, for example by heating, controlled impurity introduction, or exposure to energetic particles during the deposition of the associated organic layer. The energetic particles can be excited, for example, thermally or by RF plasma.

  FIG. 4 shows an optoelectronic device 400 manufactured according to an embodiment of the method of the present invention. The device 400 can include a substrate 410, a first electrode 420, a first layer 430, a second layer 440, and a second electrode 450. This figure is not necessarily drawn to scale. For example, the bulk heterojunction formed by the interface of the second layer 440 on the first layer 430 is shown by the solid line in FIG. 4, but the bulk heterojunction is more accurately depicted by the schematic diagram in FIG. It is. The device 400 in the exemplary embodiment includes an anode as the first electrode 420, an electron donor layer as the first layer 430, an electron acceptor layer as the second layer 440, and a cathode as the second electrode 450. . The device 400 in another exemplary embodiment includes a cathode as the first electrode 420, an electron acceptor layer as the first layer 430, an electron donor layer as the second layer 440, an anode as the second electrode 450, included.

It will be appreciated that the simple layered structure shown in FIG. 4 is provided by way of a non-limiting example, and embodiments of the present invention can be used in connection with various other structures. The particular materials and structures described are exemplary in nature and other materials and structures may be used. A functional device can be achieved by combining various layers described in different ways. Alternatively, these layers can be omitted entirely based on design, performance, and cost factors. Other layers not specifically mentioned may also be included. Materials other than those specifically described may be used. Although many examples provided herein describe various layers such as comprising a single material, it is understood that various combinations or mixtures of materials may be used. These layers may also have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 400 in one embodiment, first layer 430 transports electrons to the bulk heterojunction at the interface of layer 430 and layer 440 and may be described as an electron donor layer or an electron transport layer. Furthermore, the order of the layers may be changed. For example, in some embodiments the cathode is at the top, but in other embodiments it may be the anode. The order of the organic layers in these embodiments may also be changed accordingly.

  According to the embodiment of the method of the present invention, the first electrode and the second electrode may not be included, and the deposition of the first layer and the second layer as described above is performed only on the substrate. Also good. That is, in another embodiment of the present invention, a method for forming a bulk heterojunction includes depositing a first layer on a substrate by organic vapor phase deposition, such that the second layer is in physical contact with the first layer. Depositing a second layer on the first layer. The first layer includes a first organic small molecule material. The interface in the second layer on the first layer forms a bulk heterojunction. In a further embodiment of the present invention, a method for forming a bulk heterojunction includes depositing a first layer having protrusions on a substrate and first contacting the first layer so that the second layer is in physical contact with the first layer. Depositing a second layer over the layer is included. The first layer includes a first organic small molecule material. The interface in the second layer on the first layer forms a bulk heterojunction.

It will be understood that the various embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein can be replaced with other materials and structures without departing from the spirit of the invention. In addition, the method of the present invention may include other known processing steps used in the fabrication of optoelectronic devices. Also, the various theories as to why the invention works are not intended to be limiting. For example, the theory regarding charge transport is not intended to be limiting.
[Experiment:]

Particularly exemplary embodiments of the invention will now be described. It will be understood that the particular methods, materials, conditions, processing parameters, apparatus, and the like are not necessarily limiting on the scope of the invention.
[Example 1:]

Organic vapor phase deposition was used to deposit CuPc (electron donor material) on silicon (substrate) at an intrinsic substrate temperature of about 60 ° C. As can be seen in the scanning electron micrograph shown in FIG. 3 (a), the deposited layer of CuPc had a high surface area-volume ratio.
[Example 2:]

Organic vapor phase deposition was used to deposit CuPc (electron donor material) on silicon (substrate) at an inherent substrate temperature of about 100 ° C. As can be seen in the scanning electron micrograph shown in FIG. 3 (b), the deposited layer of CuPc had a high surface area-volume ratio.
[Example 3:]

Organic vapor phase deposition was used to deposit CuPc (electron donor material) on indium tin oxide (electrode) at an inherent substrate temperature of about 100 ° C. As can be seen in the scanning electron micrograph shown in FIG. 3 (c), the deposited layer of CuPc had a high surface area-volume ratio.
[Example 4:]

Organic vapor phase deposition was used to deposit CuPc on the silicon substrate. The source evaporation temperature is 440 ± 5 ° C., the substrate temperature is 100 ± 5 ° C., the nitrogen carrier gas flow rate is 30.0 ± 0.1 sccm, and the chamber pressure is 0.45 ± 0.01 Torr. . The growth period is 10 minutes. FIG. 5 shows a scanning electron microscope (SEM) in island growth mode in addition to the Stranski-Krastanov layer that produces a thin but continuous paint layer and short needle combination. This dense paint layer is believed to prevent direct contact between the acceptor material and the anode.
[Example 5:]

Organic vapor phase deposition was used to deposit CuPc on electrodes coated with indium tin oxide under the same conditions as in Example 4. FIG. 6 shows a scanning electron micrograph on the surface of the CuPc film.
[Example 6:]

Organic vapor phase deposition was used to deposit CuPc on indium tin oxide coated electrodes. Structures containing very dense short needles are suitable as the bottom layer of the bulk heterojunction. The source evaporation temperature and the substrate temperature are 425 ± 5 ° C. and 100 ± 5 ° C., respectively. The nitrogen carrier gas flow rate increases linearly from 14 sccm to 20 sccm during the 6.5-minute growth period, and the chamber pressure increases from 0.18 Torr to 0.70 Torr. The inset shows AFM images of the same material. The root mean square (RMS) surface roughness is 2.7 nm. FIG. 7 shows densely distributed short needles with an average length of 35 nm and a diameter of 30 nm.
[Example 7:]

  Vacuum thermal evaporation was used to deposit CuPc on the electrode coated with indium tin oxide. FIG. 8 shows the surface of a 500-thick CuPc film. The inset shows an AFM image of the sample with an RMS roughness of 0.8 nm. All scale bars are 500 nm.

The X-ray spectrum of the CuPc film of OVPD in Example 6 is shown in FIG. 9 (a), and the film grown by vacuum thermal evaporation is the same as that in Example 7 as shown in FIG. 9 (b). is there. The presence of the β-CuPc phase is confirmed by the diffraction peak at 2θ = 6.7 °. The domain size is calculated to be 20 ± 5 nm from the full width at half maximum (FWHM) of the diffraction peak, and each small protrusion in FIG. 7 is inferred to be a single CuPc microcrystalline region.
[Example 8]

The growth of CuPc in Example 6 was performed without exposing the interface to the atmosphere following the 500 ± 25 mm thick PTCBI layer. In order to ensure a flat surface, the source material was heated to 462 ± 3 ° C., while the substrate was maintained at 16 ± 5 ° C. The N2 flow rate was fixed at 150 ± 1 sccm for 10.4 minutes and the chamber pressure was 0.58 ± 0.01 Torr. A 100 mm thick BCP exciton blocking and electron conducting layer and a 1000 mm thick Ag 1 mm2 annular cathode contact deposited through a shadow mask are grown by conventional vacuum thermal evaporation to complete the PV cell. did. FIG. 13 shows an SEM image on the planarized surface. The inset shows a cross-sectional view of the PV device. The PV device has a glass layer, an ITO layer, a CuPc / PTCBI / BCP (700Å) layer, and an Ag (700Å) layer. The scale bar is 500 nm.
[Comparative example]

An ITO (450Å) / CuPc (500Å) / PTCBI (1000Å) / BCP (1000Å) / Ag device having a flat heterojunction was produced as a comparative example. A flat CuPc layer was deposited for 3 minutes at a source temperature of 445 ± 3 ° C., a substrate temperature of 3 ± 5 ° C., and a N 2 flow rate of 100 ± 1 sccm. PTCBI was deposited under the same conditions used in the bulk heterojunction device.
[Table 1]: Performance comparison aa illuminance of several ITO / CuPc / PTCBI / BCP / Ag photovoltaic cell structures is 1 sun (100 mW / cm @ 2) simulated with AM1.5G for all four devices. .

The current density-voltage characteristics in a bulk double heterojunction PV cell as a function of illumination are shown in FIG. A performance comparison of this bulk heterojunction with other double heterojunction CuPc / PTCBI PV cells is summarized in Table 1. The short circuit current is approximately twice that obtained for vacuum deposited or OVPD flat heterojunction PV cells. Furthermore, it is approximately 20% higher than the “thermodynamically driven” bulk heterojunction shown by annealing the mixed CuPc / PTCBI layer reported previously. The dependence of reverse bias photocurrent on the grown bulk heterojunction is greatly reduced from that observed for annealed devices. Adjustment of forward bias dark current density with the modified ideal diode equation (1) yields a series resistance of RSA = (2.2 ± 0.1) Ωcm 2, but obtained from a random bulk heterojunction device. The obtained value RSA is smaller than (60 ± 10) Ωcm 2.
This suggests that direct resistance due to amorphous growth, or obstacles to carrier collection, are suppressed in OVPD grown bulk heterojunction cells.

The dependence of the performance characteristics simulated with AM 1.5G solar illumination is shown in FIG. The open circuit voltage is V _OC = (0.50 ± 0.03) V at 1 sun (100 mW / cm 2). Given that this is a feature of the material system used, V _OC is approximately the same for all CuPc / PTCBI cells compared in Table 1. Other suitable materials in these devices may exhibit an open circuit voltage V _OC of about 0.4 to about 1.0 V and a current density Jsc greater than 9 mA / cm 2. FIG. 15 shows that for a device with similar V _OC , the bulk heterojunction device controls the fill ratio of OVPD growth to FF> 0 for irradiation in the range of 0.01-10 sun (100 mW / cm 2). .5. The combination of high photocurrent density and FF results in a high external power conversion efficiency (ηp) with a maximum at 1 sun (100 mW / cm 2) = ηp = (2.7 ± 0.1)%.

  Referring to Table 1, ηp is approximately 2.5 times higher than that obtained using an equivalent flat HJPV cell, and more than an annealed and thermodynamically driven bulk heterojunction. 1.9 times higher. This suggests that the controlled growth of the CuPc / PTCBI bulk heterojunction provides the desired increase in junction surface area without inducing increased cell series resistance.

  Although the invention has been described in connection with specific examples and preferred embodiments, it will be understood that the invention is not limited to these examples and embodiments. It will be apparent to those skilled in the art that the present invention described in the claims includes modifications to the specific examples and preferred embodiments described herein.

400 device 410 substrate 420 first electrode 430 first layer 440 second layer 450 second electrode

Claims (22)

Depositing a first layer having protrusions on a first electrode formed on a substrate;
Depositing the second layer on the first layer such that the second layer is in physical contact with the first layer;
Depositing a second electrode on the second layer to form an optoelectronic device;
The first layer includes a first organic small molecule material;
The interface by physical contact between the first layer and the second layer is located between the first electrode and the second electrode and is separated from the first electrode and the second electrode. A bulk heterojunction is formed,
The minimum dimension of the protrusion in a direction parallel to the plane of the substrate is between 1 and 5 times the exciton diffusion length of the first organic small molecule material;
The method for manufacturing an optoelectronic device, wherein the bulk heterojunction between the first layer and the second layer is not exposed to the outside of the first layer and the second layer.   The method of manufacturing an optoelectronic device according to claim 1, wherein the second layer includes a polymer or a semiconductor material.   3. The method of manufacturing an optoelectronic device according to claim 2, wherein an interval between the protrusions is between 1 and 5 times an exciton diffusion length of the second layer.   The method of manufacturing an optoelectronic device according to claim 1, wherein the second layer includes a metal. The first layer having the protrusion is deposited on the first electrode by organic vapor phase deposition,
The minimum dimension of the protrusion in a direction parallel to the plane of the substrate is at least less than 5% of the thickness of the device;
The method of manufacturing an optoelectronic device according to claim 1, wherein the second layer includes a flat surface.   6. The optoelectronic device according to claim 5, wherein the first layer is an electron donor layer, the first electrode is an anode, the second layer is an electron acceptor layer, and the second electrode is a cathode. Method.   6. The manufacturing of an optoelectronic device according to claim 5, wherein the first layer is an electron acceptor layer, the first electrode is a cathode, the second layer is an electron donor layer, and the second electrode is an anode. Method.   The method of manufacturing an optoelectronic device according to claim 6, wherein the first electrode includes ITO, the first layer includes CuPc, and the second layer includes PTCBI.   The method of manufacturing an optoelectronic device according to claim 8, wherein a source evaporation temperature for the deposition of the first layer is at least 400 ° C. 10.   The method of manufacturing an optoelectronic device according to claim 8, wherein the temperature of the substrate for depositing the first layer is less than 40 ° C. 10.   9. The method of manufacturing an optoelectronic device according to claim 8, wherein the nitrogen gas carrier flow rate for the deposition of the first layer is in the range of 10 sccm to 200 sccm.   9. The method of manufacturing an optoelectronic device according to claim 8, wherein a chamber pressure for depositing the first layer is 0.15 Torr-0.80 Torr.   The method of manufacturing an optoelectronic device according to claim 8, wherein a source evaporation temperature for the deposition of the second layer is at least 400 ° C.   The method of manufacturing an optoelectronic device according to claim 8, wherein the temperature of the substrate for the deposition of the second layer is less than 25C.   9. The method of manufacturing an optoelectronic device according to claim 8, wherein a nitrogen gas carrier flow rate for the deposition of the first layer is at least 100 sccm.   The method of manufacturing an optoelectronic device according to claim 8, wherein the chamber pressure is at least 0.50 Torr.   The method of manufacturing an optoelectronic device according to claim 6, further comprising depositing the third layer on the second layer such that the second electrode is deposited on the third layer. The first electrode comprises a ITO, the first layer comprises CuPc, and the second layer comprises a C _60, a manufacturing method of an optoelectronic device according to claim 6. 6. The method of manufacturing an optoelectronic device according to claim 5, wherein the device has an external power conversion efficiency of at least 1.5% under 100 mW / cm < ² > (AM1.5G) illumination. Depositing a charge recombination layer on the second layer;
Depositing a third layer with protrusions on the second electrode by organic vapor phase deposition;
Depositing the fourth layer on the third layer such that the fourth layer is in physical contact with the third layer;
Depositing a third electrode on the second layer to form the optoelectronic device;
The third layer includes a third organic small molecule material;
The minimum dimension of the protrusion in a direction parallel to the plane of the substrate is at least less than 5% of the thickness of the device;
The interface between the fourth layer and the third layer forms a bulk heterojunction,
The method of manufacturing an optoelectronic device according to claim 5, wherein the fourth layer includes a flat surface. Depositing an electron-hole recombination region on the third layer;
Depositing a fourth layer by organic vapor phase deposition on the electron-hole recombination region;
Depositing the fifth layer on the fourth layer such that the fifth layer is in physical contact with the fourth layer;
Depositing an exciton blocking layer on the fifth layer;
Depositing the second electrode on the fifth layer to form the optoelectronic device;
The fourth layer includes a fourth organic small molecule material;
The interface of the fifth layer on the fourth layer forms a bulk heterojunction;
The method of manufacturing an optoelectronic device according to claim 17, wherein the fifth layer includes a flat surface.   2. The method of manufacturing an optoelectronic device according to claim 1, wherein a height of the protrusion is equal to at least half of a minimum dimension of the protrusion in a direction parallel to a plane of the substrate.